The Reaction of Enaminones with Grignard Reagents: Synthesis of α,β-Unsaturated Ketones

Abstract

Enaminones in toluene react with Grignard reagents in tetrahydrofuran at 0–25 °C, to give selectively and with high yields the corresponding α,β-unsaturated ketones.

Notes

Preparation of 3-(2,2-dimethyl ethoxy) propylmagnesium chloride 3b: A 250ml two-necked flask was charged with 4.84g (200mmol) of magnesium in 20ml of anhydrous THF under an argon flow. To initiate the reaction 0.2ml of 1,2-dibromoethane was added. When the solvent was refluxing, a solution of 10g (66mmol) of 3-(2,2-dimethyl ethoxy) propylchloride and 2ml of 1,2-dibromoethane in 100ml of anhydrous THF were added over 1h. After additional stirring under reflux for 2h, the solution was used immediately.

The Enaminone 7 was obtained in 4 steps as shown in the Scheme 2.

Scheme 2

For the first step see: Wohl R.A., Synthesis, 1974, 38. For the second step see: Frimer A.R., Synthesis, 1977, 578. For the oxidation step see: Mancuso A.J., Swern D., Synthesis, 1981, 165. For transformation of the monoprotected diketone to the corresponding enaminone 7 see ref. 9.